Saturday, June 25, 2011

Human nature or human natures?

Most evolutionary psychologists share a belief in one key concept: the environment of evolutionary adaptedness (EEA), i.e., the ancestral environment that shaped the heritable mental and behavioral traits of present-day humans. It is usually placed in the African savannah of the Pleistocene, long before our ancestors began to spread to other continents some fifty thousand years ago. Thus, later environments have not given rise to new traits through genetic evolution.

This belief rests on two arguments: 1) such traits are complex and therefore evolve too slowly to have substantially changed over the past fifty thousand years; 2) because the same time frame has seen our species diversify into many environments, recent traits should tend to be environment-specific and hence population-specific, yet such specificity seems inconsistent with the high genetic overlap among human populations. Both arguments are weaker than they seem. New complex traits can arise over a relatively short time through additions, deletions, or modifications to existing complex traits, and genetic overlap can be considerable even between species that are morphologically, behaviorally, and physiologically distinct.

There is thus no conceptual barrier to the existence of EEAs in post-Pleistocene times. Such a paradigm could shed light on such research topics as the visual word form area, reproductive strategy, predisposition to violence among young men, and personality traits. Eventually, a multi-EEA model may dominate evolutionary psychology, perhaps after an interim period of accommodation with the current model.

17 comments:

Chuck
said...

It might be helpful to clarify (for the readers and me) the difference between population specific EEAs and frequency differences in shared EEAs. (i.e. Penke. "Bridging the gap between modern evolutionary psychology and the study of individual differences":

"If adaptations were to vary between members of the same species, different individuals must show different complex systems of genetic structures. If individuals with different adaptations then engaged in sexual reproduction (which should be possible for them to qualify as members of the same species), these different genetic structures would be broken up and mixed during the process of recombination, disrupting their complex organization and consequently their adaptiveness (Tooby & Cosmides, 1990a). Thus, complex evolved adaptations themselves cannot vary between individuals. However, adaptations are sometimes capable of producing different (morphological or behavioral) phenotypes under different conditions, and systems of adaptations are sometimes able to tolerate some genetic variation. ")

The issue regarding "complex evolved adaptations" is, What constitutes complexity? There must be some differences in adaptation between individuals in a population for evolution to occur. Chuck's argument rapidly reduces to a proof against the possibility of evolution.

Dobzhansky and Mayr solve the problem by positing that evolution occurs in small, sexually-isolated subpopulations. Moderate differences in adaptation can then accumulate, especially if there is some inbreeding.

The famous Russian experiment in the domestication of foxes should also be noted here. Domestication of wild foxes was completed in 20 generations. That is about 500 years of human evolution. So, it seems likely that rapid, divergent evolution in the populations that left Africa is possible.

As to the 500 years, it is now believed by some researchers that is about how long it took to fix relatively high IQs in the Ashkenazi Jews of Europe.

Surely there is some degree of genetic variation between, say, Indigenous Australians, the Inuit, and the Swedish people, despite the high genetic overlap between all human populations and the often cited fact that the amount of genetic diversity within each population is higher than the differences between them. Are changes in hair and eye pigmentation not complex enough to count as more recently evolved genetic traits? What about the narrow, long noses of most European populations, or the smooth and continuously growing hair?

@ Sykes, i've seen the show on TV science channel about those siberian researchers who selected the foxes, i thought they said they got their pedomorphic foxes in only 3 generations. I also have the issue of National Geographic, March 2011, page 43, on these pet foxes. The article reports that only 9 generations were needed to get floppier ears. Different pedomorphic traits were acquired at different time. Selecting only for 'friendliness towards humans', the russian researchers got, in order (generation):Approachability (2nd), Tail wagging(4th) and Petting (kits whimper and allow themself to be petted and carried by humans), full affinity (6th), then only morphological changes such as floppy ears and coat color variation come, such as peibaldism and star pattern on forehead (9th), curly tail (13th), shorter tail (15th).

So, indirect selection for pedomorphy/neoteny (via cuteness) can be quite fast, but there is a big problem:none of these pedomorphic foxes could survive in the wild. For humans to select on themselves for pedomorphic traits in postglacial europe, while staying fit at the same time, some of these traits must have given them a selective advantage. Peharps being smarter.

I quote the article: "They didn't select for a smarter fox but for a nice fox, says Hare. But they ended up getting a smart fox".

Re Ben 10's comment: " 'They didn't select for a smarter fox but for a nice fox, says Hare. But they ended up getting a smart fox.'

For humans to select on themselves for pedomorphic traits in postglacial Europe, while staying fit at the same time, some of these traits must have given them a selective advantage. Peharps being smarter "

I think you're on to something there but you've got a bit confused, the morphic traits (including light coat colors) were a unexpected side effect in the in the Russian fox taming experiment.

As I understand it Peter is saying that hair skin and eye color along with face shape were the focus of sexual selection of females. So being cute and cuddly would not have been selected for, at least not directly. The data about blue eyes preventing masculinization dovetails with the fox taming resuts I think.

The realy interesting question to my mind is whether selection for light eyes hair and skin contributed toward creating a potential for humans to become nicer and smarter.

Even within Britain there would be a considerable difference between the EEA's until the mid 18th century. The Highlands were completely lawless until then.

"So, if poverty was one keynote of Highland life, war and violence was another. It is what made the Highlander admired, and feared.

Daniel Defoe watched them walk thestreets of Edinburgh. They are formidable fellows, all gentlemen, will take no affront from any man, and insolent to the last degree. But he also noted the incongruity of one of these proud men with his weapons and tartan (another myth: genuine Highlanders wore plaids in any color that pleased them, regardless of their clan) walking as upright and haughty as if he were a lord, while driving a cow in front of him. Duels, murder, and feuding were constants in the Highlands, as was scorning, or taking food and shelter by force from tenants of other clans when a feud was under way."

Tod, you'r correct, the foxes were selected for behavior and ended up with pedomorphic traits, some with apparent decrease fitness compared to wildtype, such as shortened jaw and smaller canines.How much smart, or smarter, were these pet foxes compared to WT, I don't know. I actually always thought that wolves were smarter than their tame cousins the dogs, and that it was the case for all wild versus tame animal, because life in the wild is more intellectually demanding than as a pet.

Obviously i don't say that the same selective mechanism was applied to human hunter gatherers, but the siberian experiment shows that you can get pedomorphic traits within 3 generations. To me the big question is how any of those traits could have spreaded if they are partially recessive and don't give any selective advantage. In the case of foxes, not only the pet traits were selected but the wildtype were eliminated from the breed.

Penke (like other EEA proponents) assumes that a species is a panmictic gene pool, i.e., the rate of gene flow between populations is so high that stable population-specific adaptations cannot develop.

What is the proof for this assumption? Inevitably, the proof is Lewontin's finding that there is much more genetic variability within human populations than between human populations.

This high degree of genetic overlap, however, is also observable between many sibling species that are nonetheless morphologically and behaviorally distinct.

How come? The paradox is easy to explain. Genes vary considerably in adaptive value, with most being of very low adaptive value. When two populations differentiate under the influence of differing selection pressures, the genetic differentiation primarily concerns a tiny fraction of the genome, i.e., those genes that are being pushed in different directions by the two sets of selection pressures. The rest of the genome remains pretty much the same in the two populations, the differences being minor and usually due to stochastic factors (founder effects, genetic drift, etc.).

Answer: the rate of gene flow between human populations has not been sufficient to prevent the evolution of complex population-specific anatomical traits. Why would things be any different for complex behavioral traits?

Wilson,

She doesn't like the photo either. Says it makes her nose look too big. By the way, she's not a girlfriend. She's a 'wife'.

Maybe epsilon males like yourself don't know the difference.

Sykes, Ishtara,

Good point!

Tod,

How would you explain the high intelligence of many dark-skinned south Indians? Bangalore has become a major software center because of the relatively large number of high IQ individuals.

I agree that there is a rough correlation between mean intelligence and latitude, but I don't think the mediating factor is skin color.

"...Bangalore has become a major software center because of the relatively large number of high IQ individuals..."

You overestimate IQ, Peter. This example is just an opportunistic use of AVERAGE human cognitive capabilities and of a NORMAL education system (i.e. not like in the US), designed and organised by white high IQ people. Same for Ashkenazis. I've been teaching in the US, middle and high schools, very ethnically diverse, very hard. The education system is discriminatory against WHITE kids to the extreme. These poor kids are forced to work in an inapropriate, violent, loud, unsafe environment. These kids are also led to believe the same stereotypes about asians being smart and themselves not smart. I try to remind them that 40 years ago, without any asians, the US were able to bring a man on the moon, mostly using german technology 'acquired' during the war, i.e, without ashkenazi technology either. How could have modern white kids lost 30 points of IQ in 40 years? The truth is, the 'system' enforces these stereotypes of smart-math-lovers asians because it needs to delocalise thinking and decision out of the white male mind. Why? because this mind is antithetic with the 'system' and the 'system' can't coexist and won't survive with it. It's a war for survival, as simple as that. So the US school produces kids who can barely focuse 3 minutes and who learn maths by playing 'educational' shoot-them-up videogames, on purpose. Now the 'system' can opportunistically claim it is in dire need of high IQ individuals, anywhere in the world. High IQ Bangalore is just in fact an averaged IQ person, but who can focuse normally, and who is not a future threat, politicaly and ideologically, for the 'system'.

Please, Wilson troll, do not troll me unless you have been teaching in Washington dc or LA suburb.Recently a female teacher has been fired for ranting, anonymously with a pseudo (thanks for freedom of speech), that her school produces pre-criminal individuals. I confirm she is right. In many schools that i've been, the schools produce an amazing amount of criminal behavior: how to cheat, lie and navigate the system until more agressive beahviors. This mostly concerns minorities, latinos and blacks. So in addition to white kids unable to compete with averaged IQ Bangalories, minorities perpetuates a dysfunctional society. Please, Wilson, if you are youself a minority, make an effort to understand that the 'system' plays us all.

The US kids are not average either. They are made to be underperformers because it make sense within the rational of the 'system'. My point is that a lot of the actual situation is completely artifial and has nothing to do with the real capabilities and skills of such and such ethnic group in a fair darwinian competition. I see one historical precedent to this situation but it's not PC to mention. So, of course there are bright individuals in Bangalore, that's not the point, let's say the economic situation in the US becomes so bad and the US salaries so low that India becomes comparatively uncompetitive, and the bangalory software business shifts to Finland, you can't use this to make a point about Finish people suddenly being very smart and Bangalory people becoming stupid or lazy.Too much of what's going on is twisted and is profitable only for a few elite. In general,those who got positions through AA in the US tend to defend and reinforce this system, since they benefit from it, they will pretend for example that bright indivuals with high IQ abroad justifies delocalisation and they will do and say everything politically correct to keep the status quo.I say the country who sent men on the moon 40 years ago without asian and ashkenazi technology is perfectly capable of producing bright individuals from a pool of 350 millions people, but the elite has no interest in this to happen.

"This belief rests on two arguments: 1) such traits are complex and therefore evolve too slowly to have substantially changed over the past fifty thousand years; 2) because the same time frame has seen our species diversify into many environments, recent traits should tend to be environment-specific and hence population-specific, yet such specificity seems inconsistent with the high genetic overlap among human populations."

Lactose tolerance.

If a trait provides the difference between life and death and people are placed in a situation where that selective pressure is applied e.g. people with 80% intolerance are pushed by invaders into an environment where they have to rely on milk as a food supplement or starve. A shift to 80% lactose tolerance could happen within a few generations.

The time it takes depends on the extremity of the selection pressure.

Similarly if certain kinds of impulsive behavior in bronze age Peking got you sawn in half by a big dude in a black mask then the frequency of impulsive alleles might go down and the frequency of restraining alleles might go up over time.

."To me the big question is how any of those traits could have spreaded if they are partially recessive and don't give any selective advantage."

More co-operativeness?

This would be mainly useful in social animals and in proportion to how important co-operativeness was in a particular environment.

If you took a bunch of chimps in a safe environment and instead of breeding them for intelligence, bred them solely for niceness instead i wonder what would happen?

I think you'd get more co-operativeness. Would that in turn somehow create better conditions for selecting for higher IQ as a multiplier?

If co-operativeness gave a benefit x and high IQ acted as a multiplier (e.g. 1.2 times x) then as x tended to zero the benefit of higher IQ would shrink but as x grew larger the benefit of larger IQ would increase also.

."the rate of gene flow between populations is so high that stable population-specific adaptations cannot develop."

Lactose tolerance again and a million others. The medical consequences of keeping the truth covered up and preventing medicines being designed for specific populations are probably too big for all but the most extreme blank-slaters to swallow.

."How would you explain the high intelligence of many dark-skinned south Indians? Bangalore has become a major software center because of the relatively large number of high IQ individuals."

I don't disagree with your basic point re skin color but if this stuff is all about frequencies then 6% of a billion is larger than the total population of most european descended majority countries. Both averages and total numbers matter.

Welcome to my blog! For the most part, this page will be an extension of my website, with comments relating to my research. But it will also branch out into more general discussions of human evolution.